Acidic metal salt and sulfate solutions, such as aluminum sulfate ((Al2SO4)3.14H2O) solutions, commonly known and referred to as “alum,” have long been used to remove color and suspended particles, as well as organic and microbiological contaminants from water. Alum is readily available and when diluted with surface water, it can function as a coagulant, flocculent, precipitant and emulsion breaker. As a coagulant, alum removes the primary nutrient for blue-green algae in the water. This function is important because these algae remove oxygen from the water (known as biochemical oxygen demand or BOD) and thus pose a danger to fish. Alum also forms an insoluble precipitate or floccule, i.e., a floc, with the impurities in the water. The floc grows in size as it attracts suspended and colloidal particles and organic compounds present in the water. The floc settles out of the water over time and can be removed by well known techniques such as by decanting or filtration.
One of the most difficult problems in water pollution control is the growth of algae. As noted above, algal organisms exert a BOD on the water and the algal BOD can often exceed the oxygen resources of the water. Algal growths can also cause unpleasant tastes and odors in water supplies. Dissolved phosphate ions provide algae with a necessary nutrient supply. If the phosphate supply could be removed the algae would not survive or flourish in the water column and a water pollution control problem would be addressed. An additional difficulty associated with the treatment of phosphates in water is that the majority of the phosphates (50–90%) are concentrated at the sediment-water interface of an impoundment and current application techniques involving alum primarily treat the phosphates closer to the surface of the body of water. In addition, current techniques have been focused on nearly instantaneous sorption of phosphates. As a result, the body of existing products and techniques do not perform as effectively in a number of water systems, especially high energy and deep systems, and in systems that require more than just instantaneous phosphate sorption. In the former case, alum is flushed from the target waters before it can perform. In the latter case, the alum is poorly utilized in application. Also, the alum can leave an unwanted white cloud in the water for an extended period of time.
Therefore, there is a need for simple compositions, forms and methods for treating phosphate impoundments in bodies of water.